1. Field of the Invention
The present invention relates to an adjusting system for a crank angle sensor for use in internal combustion engines such as gasoline engines and diesel engines and, more particularly, to a system wherein such an adjustment is performed electrically with safety and high efficiency without moving the crank angle sensor itself.
2. Description of the Prior Art
Recently, fuel injection timing or spark timing in diesel engines or gasoline engines has been electronically controlled at an optimum in accordance with various engine operating conditions. For this purpose, a crank angle should be accurately detected since the crank angle is the essential determining factor for control of fuel injection timing or spark timing.
Generally, the crank angle is detected in the way as shown in FIG. 1. An engine crankshaft 1 is fitted at one end with a disk plate 2 which is provided on its circumference with a number of unit angle teeth 3 spaced apart from each other at regular intervals, and three reference teeth 4 each corresponding to the compression top dead center of two of six cylinders. The number of reference teeth 4 is three for 6-cylinder internal combustion engines and two for 4-cylinder internal combustion engines since every cylinder has one compression top dead center for every two rotations of the engine crankshaft. The position of a crank angle sensor 5 including an electromagnetic pick-up is precisely adjustable in the circumferential direction of the disk plate 2. The crank angle sensor 5 is fitted to a holder 6 which is fixed to part of the engine body such as an engine cylinder block. The crank angle sensor 5 produces a reference-angle signal and a unit-angle signal. The reference-angle signal goes high in level in response to each reference tooth 4, that is, each time the engine crankshaft rotates through 120 degress. The unit-angle signal goes high in level in response to each unit tooth 3, that is, each time the engine crankshaft rotates through a unit angle, for example, one degree. The reference-angle signal and unit-angle signal are converted via a common wave-shaping circuit into a reference-angle pulse signal and a unit-angle pulse signal, respectively. These pulse signals are then fed to a control unit, such as a fuel-injection-timing control unit or a spark-timing control unit, which is not shown in FIG. 1.
In this structure, however, it is rather difficult to accurately place the crank angle sensor 5 in a desired position and thus to obtain a signal indicative of the correct top dead center for each cylinder or of the required timing for each cylinder which will be used as a standard to control fuel injection timing or spark timing. Such a mounting error or detection error can be corrected as follows: A timing light is actuated to flash in synchronism with each pulse of the reference angle pulse signal from the wave shaping circuit. The light flashes are directed onto the engine crankshaft pulley and timing marks formed on an engine cylinder block to function as a stroboscope. If each of three top dead center marks formed on the crankshaft pulley does not coincide with a certain target value among the timing marks formed on the engine cylinder block, it means that there is a detection error or a mounting error of the crank angle sensor corresponding to the angle between the top dead center mark on the pulley and the target mark on the engine cylinder block. In this case, the mounting position of the crank angle sensor is manually adjusted until the top dead center mark on the pulley coincides with the target mark on the cylinder block.
However, such a mounting position adjustment of the crank angle sensor itself is quite dangerous, and thus entails quite a low operation efficiency, since there are a number of engine rotational parts in the vicinity of the crank angle sensor, such as an alternator, a compressor, an oil-hydraulic pump, a cooling fan, and driving belts thereof.